What type of valve operation is characterized by upstream line pressure acting to close the valve?

The type of valve operation characterized by upstream line pressure acting to close the valve is known as reverse acting operation. In this configuration, the valve is designed to close in response to an increase in upstream pressure, which often occurs in applications that require fail-safe mechanisms. When the upstream pressure rises, it applies force against a diaphragm or piston, resulting in the valve closing. This is particularly useful in situations where it is critical to stop flow automatically under specific conditions, such as in safety systems.

Solenoid valves, while they do use electromagnetic forces to operate, do not function based on upstream pressure to close; rather, they are opened or closed electrically when a current is applied. Direct acting mechanisms typically refer to situations where a valve opens with an increase in pressure or signal, instead of closing. A programmable logic controller (PLC) is a control system that can manage various valves and processes but does not describe a specific valve operation type linked to pressure dynamics.